Current-generation X-ray detector technology permits excellent medical imaging. Even at an X-ray dose that is advantageously low for the patient, it is possible to generate an X-ray image dataset providing acceptable image quality. This is attributable above all to a constant improvement in quantum efficiency or, as the case may be, a constant improvement in absorption properties of the X-ray detectors. For specific medical application scenarios, this improvement in detector sensitivity may also lead to negative effects on image quality. A possible problematic application case occurs when an examination subject, in particular a patient, is to be examined by X-ray imaging while at the same time a radioactive decay process is taking place in or on the body of the examination subject. This decay process generates gamma radiation. Whereas X-ray radiation denotes ionizing radiation in the form of electromagnetic waves having quantum energies between 5 keV and several 100 keV, ionizing radiation in the form of electromagnetic waves having quantum energies of more than 40 keV, typically 140 keV, is described as gamma radiation. If an X-ray examination and a radioactive decay process are in progress simultaneously in immediate spatial proximity, the X-ray detector detects not only the X-ray quanta but also the gamma radiation of the radioactive decay. The gamma radiation is superimposed as an unwanted interfering signal on the actually wanted X-ray signal. It is particularly problematic in this regard if there is an at least partial spectral overlap between the gamma radiation and the X-ray radiation. In application situations of this type, such as occur for example in brachytherapy when a radioactive substance intended for local tumor treatment is applied to a patient or its position in or on the body of the patient is to be checked subsequently, the consequence at the present time is a degradation, in some cases considerable, in image quality with regard to the diagnostic relevance of the X-ray image dataset in relation to the determined X-ray attenuation distribution.